(this wall of text brought to you by procrastination)

Canada allows appealing not guilty verdicts.

Also Norway, which is the system I know best, as do a substantial number of other European states, including e.g. Germany, France.

Norway (and most other European countries) do have forms of double jeopardy protection, but in Norway as in many other European countries as well as Canada, it does not attach until the case has been fully litigated and all appeals exhausted. Instead it prevents the government from bringing the case again once the case is _final_.

In Norway, the system has three levels. In criminal cases the lower court usually hear cases with a panel of three co-judges, two of which are lay persons selected from the jury pool. They deliberate together, and so nullification is effectively impossible at this stage as the professional judge can set aside a majority decision by the two lay judges voting together if their decision is a clear misapplication of the law. This right is used, but not frequently, given that the professional judge obviously in this system has ample opportunity to discuss the issue with the lay judges.

The higher court (lagmannsretten) will in more serious cases have three professional judges and a separate jury like in the US. In this case, nullification would be possible, but if the three professional judges unanimously believe that the evidence clearly indicates guilt, they can still set aside the jury decision. If they set it aside, the case is then retried at the same level without a jury, but with lay judges as in tingretten.

The last step is the supreme court, which only hears matters of law in the case of criminal cases, so in criminal cases an acquittal on matters of fact after (at worst) a second trial in lagmannsretten is almost certain to stand. As in the US, once the supreme court has either heard a case or refused to hear it (or neither side has appealed to the supreme court), the case is final. This is the point where double jeopardy attaches in Norway (there may be some very narrow exceptions, I'm not sure).

> Am I understanding correctly that the fact that nullification occurred would be grounds for an appeal in those jurisdictions?

I'm not a lawyer, but in general my understanding is that nullification _if proven_ would be grounds for appeal in any situation where an appeal is allowed pretty much everywhere, including in the US in civil cases.

This is also presumably the reason why we rarely hear about nullification outside the context of US criminal trials, because if/when it occurs it would need to be subtle and nobody on such a jury could really talk about it afterwards.

The problem in bringing an appeal in such cases is that given that the jury deliberations are private, substantiating appeals on such grounds can be extremely hard.

E.g. in the Apple vs. Samsung case a lot of Samsungs allegation of jury misconduct hinges on the fact that the foreman and at least one other juror (were there more?) have kept giving interviews and saying more and more things about the deliberations that are seemingly at odds with the instructions.

> My thought here is that in jurisdictions where jury nullification is normally possible and effective, it is only really effective if they give a not guilty verdict. A guilty verdict, given "just because" (or whatever), could be overturned in those jurisdictions, possibly even immediately by the judge.

You're right, it is vastly more powerful when the decision can't be appealed because they have the freedom to totally ignore evidence and instructions.

It can still happen in other situations, but it needs to at least be nominally possible to arrive at their decision while staying within the jury instructions which of course often will remove the opportunity to nullify in the type of clear-cut cases where nullification is most effectively used as a protest against unjust laws.